This invention relates to equipment for use in fluidized bed processes and more specifically to fluidize bed process vessels which utilize multi-stage arrangement of cyclone dust separation equipment, for example, Fluid Catalytic Cracking Unit reactors and regenerators. This separation equipment is used to separate particulates such as catalysts from hot gas.
In current practice in fluidized bed process vessels, multi-stage cyclone systems are widely used. These cyclone systems are usually in two stage arrangements with some installations utilizing three stages. In virtually all these set ups the number of cyclones, i.e., cyclone separators in each stage is the same, with each cyclone of a stage directly connected to a companion cyclone of another stage thus, forming an individual set, with no direct connection to any other cyclones in the system. The catalyst separated by the cyclones is conveyed to the bottom of the vessel through pipes called dip legs.
In recent years there has been a development of so called "Closed Cyclone" systems for FCC units. This type of system uses a design which minimizes contact time between hydrocarbon vapors and catalyst which results in enhanced productivity of the FCC refining process. Therefore, many refiners who have existing facilities desire to make use of this procedure by modifying their facilities to adopt this technology. New FCC plants can also make use of this improvement in their initial design.
At this time these "Closed Cyclone" systems utilize two stage of cyclones, a "riser" cyclone stage followed by an additional "upper" cyclone stage which separate all but a residual amount of the catalyst before the hydrocarbon vapors leave the reactor vessel. In these systems, each riser cyclone is connected to a companion upper cyclone resulting in the same number of cyclones in each stage as already described.
In some vessels the space available to accommodate the desired cyclone system is restricted, particularly in vessel overall headroom, which can result in interference between the bottom of the upper cyclones and the top of the riser cyclones. Thus, in these circumstances it is desirable to minimize cyclone overall height. One way this can be accommodated is to utilize smaller diameter cyclones, which, of course, then requires use of more cyclones in parallel to maintain desired cyclone capacity.
Since each riser cyclone is directly connected to its companion cyclone, this normally compels the connected cyclones to be in close proximity of one another. In many vessels, this constraint can result in difficulties related to interferences among the cyclones; between the upper cyclone dip legs and the riser cyclones; between the upper cyclones and/or dip legs and the riser cyclone support structure. Also this constraint may require locations of the cyclones in such a manner which results in unacceptable slopes of the dip legs, endangering proper catalyst flow that is required to direct the separated catalyst to the lower portion of the vessel.